The LM3551 and LM3552 are fixed frequency, current mode step-up DC/DC converters with two integrated NFETs that can be used for precision LED brightness control The devices are capable of driving loads up to 1A from a single-cell Li-Ion battery.
The LM3551 and LM3552 can drive one or more high current flash LEDs either in a high power FLash mode or a lower power Torch mode using the Torch/Flash pin. A programmable Timeout function on the FTO pin forces the internal NFETs to turn off after a certain user defined time. An external SD pin (LM3551) or EN pin (LM3552) is available to put the device into low power shutdown mode. During shutdown, the feedback resistors and the load are disconnected from the input to avoid leakage current paths to ground.
User programmable soft-start circuitry has been integrated to eliminate large inrush currents at start-up. Over-voltage protection circuitry and a 1.25MHz switching frequqncy allow for the use of small, low-cost output capacitors with lower voltage ratings.
The LM3551 and LM3552 are available in a low profile 14 pin LLP package.
The LM3552 evaluation board provides an example of a high current white LED flash driver. Torch (continuous) mode and Flash (pulse) mode control is provided through a single dedicated control pin. On this evaluation board, the torch current is set to 200mA to allow continuous operation, whereas the flash current is limited to a one second, 700mA pulse. Many flash specific safety features have been integrated into the LM3552 architecture and are utilized on the evaluation board design (Over-voltage protection, Flash Time-Out, Current Limit, etc.) For more information, please refer to the data sheet and applications note.